From the state of art nozzle assemblies are known for mounting in a handle of a pipette either mechanical or electronic and for cooperation with other mechanisms realizing different functions in the pipette, including a pipette exchangeable tip ejection mechanism and a drawing up and discharging mechanism of pre-set values of a liquid volume.
Many known nozzle assemblies comprise a one-piece nozzle which lower part is shaped respectively, preferably conically, for receiving exchangeable tips and which upper part is mounted in a pipette handle. Inside the nozzle a plunger is slidably mounted. The plunger is coupled with a pipetting rod and further with a push-button of the drawing up and discharging mechanism. For ensuring a correct operation of the pipette and for drawing up or discharging by the pipette repeatable, proper and intended volume values of a liquid, the nozzle assemblies comprise technical means which seal the plunger in the nozzle. In case of the one-piece nozzle, sealing means are situated inside the pipette nozzle in the vicinity of, the most often, the end of the lower part of the nozzle. An access to the sealing means which require cyclic maintenance is difficult in the known nozzle assemblies with the one-piece nozzle.
Effectiveness of a sealing function of the plunger sealing means in the nozzle of the nozzle assembly in the course of different pipette modes, especially in PIPETTING MODE, ADJUSTMENT MODE and CALIBRATION MODE, is a critical issue for correctness of the whole pipette operation. Another important issue for a pipette user is an accessibility to the sealing means to perform necessary maintenance activities in MAINTENANCE MODE of the pipette.
From the patent application No. U.S. Ser. No. 10/239,725 that has been published under No. US 2003/0101831 A1, the nozzle assembly for mounting in a pipette handle is known, which nozzle assembly comprises a nozzle two-piece body consisting of the upper part in the form of the holder and the lower part in the form of the nozzle. The holder and the nozzle are coupled detachably, preferably by means of a screwed connection. In the nozzle two-piece body a plunger is slidably mounted. The plunger cooperates via engaging means with a pipetting rod of a pipette drawing up and discharging mechanism, which is placed in the pipette handle. Between the body pieces i.e between the holder and the nozzle, sealing means are arranged, which are in contact with the holder, the nozzle and the plunger and are compressed between the holder and the nozzle.
In the nozzle assembly disclosed in the publication No. US 2003/0101831 A1, a pressure of sealing means to a nozzle abutting surface and to a plunger working part is realized by means of a releasable connection, preferably a thread connection, between a nozzle and a nozzle holder, and is exerted as a result of a compression of the sealing means between the nozzle abutting surface, the holder abutting surface and the plunger working part. The technical means which serve to exert a proper pressure force are, in case of the screwed connection between the nozzle and the holder, a nozzle external thread and a nozzle holder internal thread. As a result, the pressure force is dependent on dimensions and working tolerances of the nozzle and the nozzle holder. For obtaining a desired value of the pressure force of the sealing means in the form of a sealing ring to the nozzle, to the nozzle holder and to the plunger, the nozzle and the nozzle holder have to be made under a high technological regime so that their dimensions are contained in the accurately determined tolerances.
In this known nozzle assembly, the pressure force of the sealing means to the nozzle, to the holder and to the plunger depends on the manner of coupling the nozzle with the holder, and in the embodiment illustrated the pressure force depends on a degree of screwing the nozzle into the holder. In the case when the nozzle is screwed into the holder improperly or when the nozzle becomes loose as a result of an incorrect operating of the pipette, a leakproof condition between the plunger working part and the nozzle, which is necessary for the correct pipette operation, will not be met.
The manner of mounting the sealing means in the nozzle assembly, which is known from the publication No. US 2003/0101831 A1, makes it impossible to change a type of the sealing means applied and described in this document and further to apply the other type of the sealing means.
In the nozzle assembly of such a structure, after disengagement of the nozzle from the holder in MAINTENANCE MODE of the pipette, the sealing means remain stationary in relation to the plunger and the holder, and are not slid outside automatically from the holder abutting surface, and thus for the maintenance of the sealing means an user has to draw manually the sealing means outside the holder by pressing a pipetting push-button of the pipette and by knocking or shaking with the pipette.